Interpretive Summary: Silage inoculants (lactic acid bacteria) are commonly added to crops going into silos, helping guarantee a good fermentation and preservation in the silo. Often this addition of bacteria at ensiling increases the milk produced by cows fed these inoculated silages, but we do not understand why. We ensiled alfalfa and corn with three treatments: without additive, with a bacterial strain that has been shown to increase milk production, and with formic acid (a chemical treatment that is known to help preserve protein during ensiling). Both the inoculant and formic acid treatments improved the preservation of protein in silage compared to that in the untreated silages. We then measured how well these silages were digested when placed in fluid taken from the main stomach, the rumen, of several cows. Both the inoculant and formic acid treatments increased the amount of rumen bacterial protein produced. This increase in rumen bacteria could potentially explain the increase in milk production from inoculated silage because rumen bacteria are an excellent source of protein for the cow and the milk she produces. These results bring us closer to understanding how inoculants improve milk production and provide farmers greater confidence that these products can be beneficial in making high quality silage.

Technical Abstract:
Four alfalfa trials, one corn, and one bmr corn were treated with no inoculant (Control), Lactobacillus plantarum (MTD/1) and formic acid (FA), ensiled in 1-L mini-silos, and fermented for 60 d at room temperature (22 C). Mini-silos were opened and analyzed for fermentation characteristics and soluble N fractions. A fraction of wet silage from each mini-silo was ground to 4 mm and frozen at -20 C. In vitro gas production, volatile fatty acids (VFA), microbial biomass (MB), and bacteria non-ammonia N (NAN) using 15N as marker were measured in each wet silage sample after 9 h incubation. In four of the six trials (three of the alfalfa trials and the corn silage), silage fermentation products and pH indicated good preservation across treatments. However, two treatments in the bmr corn silage trial had elevated ethanol concentrations, and the second alfalfa trial had pH above 5.0 in two of the treatments. The combined analysis of the four trials with good preservation across all three treatments showed that soluble N fractions were different among treatments. The FA and MTD/1 treatments had lower ammonia N and free amino acids N than control. The FA treatment was lower in soluble nonprotein N, but greater in peptides than control. The pH was lower in FA (4.25), followed by MTD/1 (4.28), and control (4.38). In vitro gas and VFA concentrations were not different among treatments (P > 0.05). The FA and MTD/1 treated silage yielded greater bacterial NAN than control. Even though MB was not different among treatments (P > 0.05), MTD/1 and FA were numerically greater in MB than control. These findings suggest that MTD/1 preserved more true protein during silage fermentation than control, which in turn increased rumen in vitro microbial growth.